Such an energy supply system and a method for operating an energy supply system are known from wind power plants, for example, but also from electric drives or hybrid drives of motor vehicles.
To be able to make available the power and energy required for the respective application, storage modules configured as storage cells are connected in series and to some extent also in parallel. A plurality of storage modules is connected in series to achieve the high operating voltage required in the motor vehicle for the electric motor of the electric drive or hybrid drive by adding up the voltage of the individual storage modules configured as storage cells in the electrical energy storage system, i.e., the total voltage of same. The energy storage system is configured, for example, as a battery system having a plurality of battery cells. The high operating voltage may be decoupled from the following energy transmission devices, which are configured as electronic power components such as inverters. Since the total output current of the electrical energy storage system configured as a battery system flows in each of the battery cells in a series connection of the storage modules configured as battery cells, the charge transport taking place through electrochemical processes within the battery cells, the failure of a single battery cell in the extreme case means that the entire configuration is no longer able to provide electrical energy for a downstream electrical device.
An ascertaining device configured as a so-called battery management system is generally used to allow prompt detection of an imminent failure of a battery cell; this system is connected or connectable to both poles of each battery cell and determines such operating parameters as the voltage and temperature of each battery cell at regular or selectable intervals and determines from this at least one state variable such as the state of charge (SOC) of the cell. However, high voltages and/or high currents flow at the poles of the battery cells due to the series connection and/or parallel connection of the cells. This requires a great effort with little flexibility of the electrical operating data of the battery system at the same time.
In addition, the following problems arise for a series connection of a plurality of battery cells to achieve a high total voltage: for different operating states of the device to be operated by the battery, e.g., an electric machine, conditions for the operating voltage to be supplied, the maximum current and the stored energy are formulated, which may be combined only when a larger number of battery cells is linked together than would actually be necessary to meet the requirements. This increases the price as well as the weight and volume of the battery system, which are problematical in particular in an electric automobile. Assembly of the battery system, i.e., connecting the individual cells to one another, takes place at high total voltages of up to 1000 V because of the voltages of the individual battery cells which are added up due to the series connection, which is why a replacement of the battery system, individual cells or modules cannot be carried out in local workshops or in the case of a stationary application it may be carried out only by specially trained personnel using special tools. This results in a high logistical effort for maintenance of battery systems in the event of a defect. In addition, parts of the ascertaining device are in contact with a correspondingly high electric potential. To switch the battery system to be voltage-free, i.e., to separate the actual battery from the load, power circuit breakers, which are typically configured as contactors and are very expensive for the high currents and voltages to be expected here, must be provided.
The object of the exemplary embodiments and/or exemplary methods of the present invention is to introduce an energy supply system and a method for operating such an energy supply system for overcoming the aforementioned disadvantages of the related art.